.myhead{
    width:100%;
    position: fixed;
    top:0;
    left:0;
    height:0.45rem;
    background:#fff;
    border-bottom:0.5px solid #b9b9b9;
    line-height: 0.45rem;
    text-align: center;
    font-size: 0.2rem;
    z-index:2;
}